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86 METALLURGY OF CAST IRON.
W, and also of the flame in the ovens, affords an experienced furnaceman much knowledge of the condition of a furnace or what results may be expected in its workings. In this respect, also in regard to explosions, the same is to be said of a brick stove as of the iron one, and a close watch is generally kept of the color and action of the gases. The gas', as it escapes from the top of a furnace in its passage downward to the iron or brick oven, is chiefly in the form of carbonic oxide and may often not have a temperature of 300 degrees of heat, although it generally ranges from 400 to 500 degrees as it passes through the "down-comer " to the ovens. This form of gas is an explosive, requiring air to make it combustible. This element it receives after it has entered the ovens, the air being drawn from .outer channels or flues in the brick work of the iron stoves, as at H and F in the brick stove; this action creates the flame in the ovens just cited, which then raises the temperature to the degrees above noted. If the gas were allowed to pass into the oven in the state in which it comes from the top of a furnace through the "down-comer" without receiving a sufficient supply of air, the gas would be of little value in raising the temperature of the blast confined in the pipes on its passage to the furnace.
The plans and working of a brick stove are as follows: The line of the arrows seen in Fig. 14 displays the various channels through which the cold blast travels after entering the brick stove at E, seen at the end of the cold blast inlet pipe. The direction of the cold blast in being heated is directly opposite to that taken by the gas cpming from the furnace to heat up the walls and various channels and checkered brickres, etc. It may also beency :|,